Under Darius, the Persian Empire became the largest of its time. As the map illustrates, the empire stretched from North Africa to India and from the Aral Sea to the Persian Gulf. It covered 7,500,000 square kilometres (2,900,000 square miles), making it comparable with the Roman Empire and the Chinese Han Empire. Its inhabitants were extremely diverse: as well as the Persians and the Medes, there were Egyptians, Greeks, Scythians, Babylonians, Bactrians and Indians, among others.

The empire was formed into provinces called satrapies, each of which was governed by a satrap on behalf of the king. A primary function of the satraps was to gather tribute; its presentation to the king is depicted on many of the stone reliefs at Persepolis. Other reliefs show the people supporting the king's throne, symbolising the extent of his power but also the cosmopolitan nature of the empire. The subject peoples are incised on the base of the famous - now headless - statue of Darius.